Elettronica Santerno SINUS/ISD 200 S-0.75, Руководство пользователя, Страница: 181 / 206

SINUS/ISD 15P0082B8
USER MANUAL
13 - 1/2
13.0 13.0 A A
PPLICATION PPLICATION
N N
OTES OTES
•
Always use gold flash relays, or others designed for low current operation (5mA), on all control wiring.
•
Remove all power factor correction equipment from the motor side of the Inverter before use.
•
Avoid using motors with low efficiency and small cos ø (power factor) as they require a larger kVA rated
Inverter to produce the correct shaft kW.
13.1 13.1 SYNCHRONOUS MOTOR CONTROL SYNCHRONOUS MOTOR CONTROL
Although intended primarily for use with induction (asynchronous) motors, Inverters can also be used for speed
control of synchronous motors. Synchronous motors can offer economic solutions in applications where tight
control of speed is required together with the low maintenance characteristics of an ac motor.
The two most common types of synchronous ac motor are
permanent magnet and wound rotor .
In contrast to induction motors, synchronous motors run at synchronous speed whether on full load or no load.
Synchronous speed is set by the frequency of the supply applied to the stator. The stator flux can be kept
constant by keeping the stator volts/frequency ratio constant, as with an induction motor.
Torque is produced in the motor by an increase in load angle between the stator and rotor fluxes. Maximum
torque occurs when the load angle approaches 90
°
. If the load angle exceeds this value then torque drops and
the motor will stall. Systems involving synchronous motors need careful design to ensure that the motor can
accelerate the load and handle transient load changes without stalling.
13.2 13.2 BRAKE MOTORS BRAKE MOTORS
Brake motors are used in applications requiring a mechanical brake for safety or other operational reasons. The
motor can be a standard induction motor fitted with an electro-mechanical brake, or it could be a special conical
rotor machine. In the case of a conical rotor machine the spring-loaded brake is controlled by the motor terminal
voltage as follows:
•
At rest the motor is braked.
•
When the motor is energised an axial component of the magnetic field due to the conical air-gap overcomes
the force of the brake spring and draws the rotor into the stator. This axial displacement releases the brake
and allows the motor to accelerate like a normal induction motor.
•
When the motor is de-energised the magnetic field collapses and the brake spring displaces the rotor,
pushing the brake disc against the braking surface.
Inverters can be used to control the speed of conical rotor brake motors since the linear V/F characteristic
maintains the motor magnetic field constant over the speed range. It will be necessary to set the FIXED BOOST
parameter to overcome motor losses at low speed (see FLUXING menu at level 3).